The invention relates generally to systems and methods for estimating material properties of a part and, more particularly to, an eddy current system and method for estimating material properties of a shotpeened part.
Components such as aircraft engine parts are protected from developing microcracks by creating a compressively stressed surface layer using shotpeening. Very briefly, shotpeening involves bombarding the surface of the part with small spherical media called shot. Each piece of shot striking the surface imparts a small indentation to the part. In order for the indentation to be created, the surface of the part must be yielded in tension. Further, below the surface, the material tries to restore its original shape, thereby producing a hemisphere of material that is highly stressed in compression. Monitoring of material properties of shotpeened parts is desirable to determine how long the part can be used before it needs to be re-shotpeened. For example, it is desirable to monitor the shotpeen residual stress depth profile of the part to assess the need for re-shotpeening of the part.
Typically, a destructive evaluation of the shotpeened part is performed to estimate the material properties of the part. However, this technique makes the part unusable and therefore requires the part to be replaced. In other applications, certain shotpeened parts may be re-shotpeened at select time intervals without assessing the need for re-shotpeening the part.
Eddy current measurement techniques may be employed to non-destructively measure the material properties of the shotpeened part. Eddy current measurement technique is based on the principle of electromagnetic induction. In one method, a drive coil is employed to induce eddy currents within the material under inspection, and secondary magnetic fields resulting from the eddy currents are detected by a sense coil, generating signals, which are subsequently processed for estimating the material properties of the part. In another method, eddy currents induced in the material under inspection produce changes in the self-impedance of a coil and by monitoring these changes one can estimate material properties of the part. However, existing eddy current measurement techniques do not account for error introduced due to surface roughness associated with the shotpeening and therefore do not provide an accurate estimation of the material properties of the part.
Accordingly, it would be desirable to develop estimation techniques that provide accurate estimation of material properties of a part. Particularly, it will be advantageous to develop a technique for accurate estimation of the material properties of a shotpeened part without damaging the part.